1. Field of the Invention
The present invention relates to a composite film, a semiconductor device employing the same and a method of manufacturing the same. More specifically, the present invention relates to a semiconductor device fabricated by applying a so-called film carrier system by utilizing a novel composite film and a method of manufacturing the same.
2. Description of the Prior Art
A conventional method of semiconductor devices on a mass production basis employed a lead frame obtained by pressing a metallic flake. However, a conventional lead frame thus pressed made it impossible to supply such lead frame in a continuous or endless manner. Therefore, U.S. Pat. No. 3,689,991 was proposed which constitutes the background of the present invention. The referenced United States patent employs a flexible film carrier as shown in FIG. 1. Such flexible film is formed by adhering a copper film 3 onto a heat resistant plastic layer 1 of such as polyimide, polyamideimide or mailer with an adhesive agent 2. Such flexible film is transferred in succession in the longitudinal direction and lead patterns each having a plurality of leads are formed, thereby to provide flexible lead frames. By employing a flexible film as shown in FIG. 1, semiconductor devices can be manufactured with higher efficiency on a mass production basis as compared with conventional employment of lead frames made of metallic flakes as punched.
However, such conventional method of manufacturing semiconductor devices utilizing a flexible film employing such conventional heat resistant plastic has not yet become popular. The reason is that organic resin such as polyimide used as a plastic layer 1 for supporting the copper films 3 is so expensive that it costs as high as approximately 50 dollars per 1 m.sup.2. In addition, even in the case where multilayer circuiting is made using such films, problems are involved. More specifically, since resin such as polyimide forming the above described plastic layer 1 has expansibility/compressibility, it becomes difficult to form pass through holes passing therethrough. Even if such pass through holes are formed, it was necessary to apply through hole plating 4 for the purpose of connecting the copper films 3 and 3 on both surfaces, as shown in FIG. 2. The reason is that the diameter of each pass through hole is susceptible of change due to expansibility/compressibility of the plastic layer 1.
On the other hand, conventionally hybrid integrated circuits have been fixed on a board made of alminum, for example. A conventional approach of employing such alminum board is of poor convenience of operation. Accordingly, another approach of utilizing such a film carrier as shown in FIG. 1 could be thought of. However, a conventional film carrier is expensive as described above and thermal conductivity of polyimide for example is poor, so that the advantage of hybrid integrated circuits that heat dissipation is good is degraded. As a result, it was impossible to utilize such conventional film carrier as shown in FIG. 1 in manufacture of hybrid integrated circuits.